1. Field of the invention
The present invention relates to a recording medium which comprises a first substance and a second substance at least, and whose optical characteristics are varied to record information by applying an external energy for reaction to at least one of the first and second substances.
2. Description of the Related Art
As a conventional optical recording medium, for example, Japanese Unexamined Patent Publication (KOKAI) No. 62-226,442 discloses an optical recording medium in which a mixture film (a single-layered film) is used as a recording film. The mixture film is composed of a low-melting point metal (e.g., In or Zn) and sulfide (e.g., GeS.sub.x). Japanese Unexamined Patent Publication (KOKAI) No. 2-152,029 discloses another optical recording medium in which a layered film is used as a recording film. The layered film is composed of a metallic layer (i.e., a first layer), which includes Al, Cu or Ag, and the other layer (i.e., a second layer), which includes S, Se or mixtures thereof.
These recording films are formed by a vapor deposition method or a sputtering method. Since the recording films exhibit reactivity, the recording films are modified chemically and/or physically by irradiating with a recording laser beam (or by applying an external energy). Accordingly, the optical characteristics of the recording films, such as the reflectance, are varied, thereby recording information.
Japanese Unexamined Patent Publication (KOKAI) No. 62-226,442 discloses to form the mixture film of the low-melting point metal (e.g., In, etc.) and the sulfide (e.g., GeS) by a co-vapor deposition method, or the like, in the preferred embodiments. However, according to the investigations carried out by the inventors of the present invention, the reaction proceeds considerably between the metal and the sulfide during the formation of the mixture film. As a result, there is a possibility that the entire reflectance of the optical recording medium decreases significantly, and this causes problems in applying the optical recording medium to practical uses.
Japanese Unexamined Patent Publication (KOKAI) No. 2-152,029 discloses the laminated construction in which the metal of high reactivity (e.g., Ag, etc.) are laminated on S. However, according to the investigations carried out by the inventors of the present invention, it can be readily judged that such a system suffers from severe chronological degradations, for instance, the layers react with each other even when information is not being recorded. Hence, it is believed that, the optical recording medium suffers from problems in practical uses. Moreover, in the preferred embodiments, the values of C/N (Carrier to Noise ratio, i.e., output level ratio of carrier to noise) are listed, but do not imply the favorable characteristics.
Thus, in the conventional optical recording media, unnecessary reactions, such as the reactions in the formation of the films and the chronological degradations, are allowed, because they use reactive recording films. Hence, the conventional optical recording media have problems in that the recording characteristics, such as the reflectance, degrade in the formation of the films and during the ordinary service.